From the Release Notes:
Installation Instructions
To install PGP Desktop on your Mac OS X system:
1. Mount the PGP Desktop disk image.
2. Double-click PGP.pkg.
3. Follow the on-screen instructions.
4. If prompted to do so, restart your system.
For additional information, including upgrade instructions, see the PGP Desktop for Mac OS X User's Guide.
Note: If you are upgrading your computer to a new major release of Mac OS X (such as from 10.5.x to
10.6.x) and want to use this version of PGP Desktop, be sure to uninstall any previous versions of PGP
Desktop before upgrading to the new version of Mac OS X and installing this release. Be sure to back up
your keys and keyrings before uninstalling. Note that if you have used PGP Whole Disk Encryption, you will
need to unencrypt your disk before you can uninstall PGP Desktop.